1. Field of the Invention
The present invention relates to flexible nanostructure electronic devices, such as nanotube sensors and transistors, and method for fabricating the same.
2. Description of Related Art
Flexible electronics or transistors are desirable for many applications. These applications include applications in flexible displays, wearable electronics, intelligent papers, and lightweight/cheap electronics. To meet these applications, it is important to have a flexible semiconducting channel. Many flexible transistors have been developed by using organic channels such as semiconducting polymers or organic crystals (e.g. crystalline pentane). The other elements of the transistor structures, such as contacts and the gate dielectric, have been made from organic materials and from inorganic materials. The core problem with these previous developments has been that the organic materials have extremely low carrier mobilities. As a result, the transconductance of these devices has been very small. Since transconductance determines the speed of a device, flexible electronics have been very slow. By contrast, nanotube carrier mobilities are extremely high. Therefore, flexible nanotube electronic devices or transistors promise to be superior to other flexible electronic devices or transistors.
Carbon nanotubes have emerged as materials of fundamental importance and great potential due to their exceptional electrical, mechanical, and thermal properties. Various proposals exist for their incorporation into devices based on thin nanotube film architectures and geometries. Very thin nanotube films could be used in fault tolerant sensor networks, thermal heat shunts, as well as for measurements of fundamental nanotube properties in cavity and optical experiments. For such applications the preparation of uniform flat nanotube films is of paramount importance.
However, certain obstacles are encountered in the manipulation of these nano-electronic or microscopic objects. The laying down of a thin film of nanotubes is not easily accomplished. One difficulty arises from the fact that nanotubes have a very poor solubility in typical solvents without the use of surfactants, impeding film-forming using carrier solvents. Furthermore, when nanotubes are suspended or dissolved in solution at low concentrations, evaporation (e.g., drying) of the carrier liquid may result in flocculation and clumping, when the local concentration of nanotubes approaches the solubility limit. Moreover, surfactants that make the nanotubes compatible with aqueous dispersions may be inappropriate for applications that require pure nanotubes. Under some situations, nanotubes can be deposited with spin coating, but for the thinnest films (<1 μm), it is difficult to get adequate uniformity. Strong intertube attractive forces, violent hydrophobicity, and low solubility at moderate concentrations all fight against typical wet chemistry techniques to make uniform films.
It is desirable, therefore, to provide flexible nanotube electronic devices or transistors and methods for making the same that overcomes the above-described shortcomings while retaining their advantages (e.g., by providing superior flexible transistors or a better way of making them).